I can only assume that, since you are putting hacking at the same level as gaming, you have no idea what hacking actually entails. A good gaming rig requires (usually) expensive components, a large monitor, nice speakers, a responsive and multi-functional mouse, and many other things you are going to spend a lot of time and money on. Contrast this with hacking, which can be done on pretty much anything, down to and including roadkill (assuming you manage to install Linux on it, which you can with enough patience).

What, did you think hacking was like in the movies? Flying through cyberspace and shooting through firewalls?

My experience with building custom rigs is pretty minimal. I have never built a gaming PC, but I have thrown together workable PCs out of essentially Frankenstein parts. My current "gamer" is one I bought stock and it works well for me.

That said, I'd start by ditching Vista for XP; as far as I have heard, XP is still best for gaming. As far as hardware goes, I can't get too specific myself, but if you are trying to do this on a lower budget, focus only on what you need. Keep the speakers you have, you probably won't need a great CD/DVD drive, etc etc. For a mouse, if you are looking for a change, I highly recommend the Logitech Mx518. Just about any monitor will do, despite what people will say. 2GB of RAM is a tad bit low. Not gonna check your processor specs, but I'd go for at least dual-core. For the graphics card, and you should just go for what's the best within your price range.

Kinda jumbled advice, but it's a start. To sum it up: Only focus on what will increase your FPS, and skimp on the rest.

You can't do much with it, if that's so. It's pretty much an expensive paperweight.

Try Goatboy's advice, but I doubt you'll be able to get much performance out of that thing without sinking a lot of money into it, at which point you may as well buy a new one. You'll definitely need to replace that power supply, though. I'm surprised the damn thing even turns on with 250W.

If you're trying to go with a good budget gaming PC, you're going to want 4GB of ram, which most older motherboards won't allow, so you're gonna definitely need a new one which will run you $100 on average for a decent one, Then you're going to probably get a new CPU to fit that socket. There's another $80 to $100. 2 X 2GM RAM is another $100 roughly, so at that point I would just build your own computer. It really isn't too expensive if you're on a budget. If you can save your current monitor, keyboard, mouse, and speakers, it can be done for roughly $600 - $700. I've never built one personally. But I've read plenty on it and watched videos on how it's done. And I've 'built' them on TigerDirect and NewEgg. It'll run you roughly the same price of an average stock PC at a store if you were to build a good, budget gaming PC